Stainless steel knife blade and process for the manufacture thereof

ABSTRACT

STAINLESS STEEL KNIFE BLADES HAVING IMPROVED EDGE HARDNESS AND CUTTING STABILITY ARE PRODUCED IN A MULTISTAGE PROCESS. A SEMI-FINISHED BLADE IS PRODUCED, E.G. BY FORGING A WORKPIECE, HAVING A RELATIVELY THICK PORTION OF METAL IN THE VICINITY OF THE EVENTUAL CUTTING EDGE. IN THIS WAY THE HARDNESS OF THE CORE MATERIAL IN THE AREA OF THE CUTTING EDGE IS NOT REDUCED IN THE FORGING PROCESS AND THE CUTTING EDGE IS REVEALED BY GRINDING OR CUTTING AWAY THE SURPLUS METAL FROM THE SEMI-FINISHED PRODUCT.

1971 ROLF-JURGEN EICKHORN 3,616,712

STAINLESS STEEL KNIFE BLADE AND PROCESS FOR THE MANUFACTURE THEREOF Filed May 18, 1970 FIG.1

FIG.2

FIGA

FIG. 3

United States Patent Offlce 3,616,712 Patented Nov. 2., 1971 3,616,712 STAINLESS STEEL KNIFE BLADE AND PROCESS FOR THE MANUFACTURE THEREOF Rolf-Jurgen Eickhorn, 51 Pfalfenberger Weg, 565 Solingen, Germany Filed May 18, 1970, Ser. No. 38,329 Claims priority, application Germany, May 21, 1969, P 19 25 846.9 Int. Cl. B21k 11/00 US. Cl. 76--104 R 6 Claims ABSTRACT OF THE DISCLOSURE Stainless steel knife blades having improved edge hardness and cutting stability are produced in a multistage process. A semi-finished blade is produced, e.g. by forging a workpiece, having a relatively thick portion of metal in the vicinity of the eventual cutting edge. In this way the hardness of the core material in the area of the cutting edge is not reduced in the forging process and the cutting edge is revealed by grinding or cutting away the surplus metal from the semi-finished product.

BACKGROUND TO THE INVENTION Table knives and domestic knives are nowadays mainly made of stainless steel. For this purpose the non-rusting steel usually requires a comparatively high carbon content, so that the blades will be sufficiently hard. Blades of this kind, however, are attacked by dish-water and detergents, particularly by those used in dish-washing machines, so that serious corrosion and similar drawbacks occur.

In the case of blades made of steels having a smaller or hardly any carbon content or of alloys of which the constituents are far more resistant, on the other hand, the desired hardness is not immediately obtained. It is true that attempts have been made to solve this problem by giving the blades a fairly ample cross-section, but they then have a squa and inelegant appearance, not in accordance with the fashionable blade shape that has become established.

SUMMARY OF THE INVENTION The purpose of the invention is to enable these disadvantages to be avoided and to provide a blade unaffected by dish-water and detergents, particularly a washingmachine-proof blade, with normal shape and cross-section but nevertheless with the necessary hardness, accompanied by elasticity, together with the desired cutting power and cutting stability.

To achieve this object the invention proposes a process for the production of stainless steel knife blades which is characterized by the fact that a semi-finished product consisting of stainless steel, with or without carbon and also of any desired alloying ingredient, is shaped with extra core-hardness, the blade being worked out of the hard core of the said semi-finished product. The invention is thus based on the realization that when stainless steels are shaped into blades or similar objects the surface of the material will be somewhat less hard, after the shaping process, than the core of the blank. In the blade production method adopted hitherto, on the other hand, the blank is depth-hardened, or the hardening is carried out in such a way that a softer elastic core is left.

In a preferred embodiment of the invention, a blank is first of all shaped, e.g. by hot forging, with a considerably greater volume than that intended for the finished blade, and this intermediate product can then be further shaped to form a semi-finished product, e.g. by the cold shaping process, the finished blade being finally worked out of the core of the said semi-finished product. The operation of working the finished blade out of the core can be effected, for example, by grinding the surplus material off the core belonging to the semi-finished product and forming the blade, thus exposing the said core. In this connection the machining can be carried out in such a way that only the material surrounding the core is shaped beyond the flow limit, thus providing a comparatively hard core surrounded by a softer outer skin. For example, the core will have a Rockwell hardness of the order of 42-50 R that of the outer skin being only about 35-42 R As the maximum hardness and durability of the blade must be in the vicinity of the cutting edge, the invention further provides that in the case of the blank and the semi-finished product the surplus of material can be the maximum in the zone corresponding to the cutting edge of the finished blade, i.e. a comparatively moderate surplus of material can be adopted in the remaining portions of the blade, so that the deformation energy can be kept fairly low. If the hardness of the-blade in the non-cutting zones is somewhat less than in the portion corresponding to the cutting edge, this does not matter, because the quality of the knife is assessed according to its cutting power and cutting stability; the flexural strength will then also be sufficient in the zones in which the aforementioned extra hardness is not obtained.

The stainless steel blank is preferably shaped, e.g. by the cold forming process, into a semi-finished product having a surrounding fin or burr. This fin, deliberately produced in the shaping process and destined to form the actual blade, is to be regarded as the fiow zone, thus acting as a clamp surrounding the core, so that in this latter the material is unable to flow in the course of the shaping process and not only retains its original strength as a result of the deformation pressure and the supporting effect of the fin but is actually increased in the strength.

This deliberately created fin thus forms a contrast to the otherwise usual forging burr, which does not exert the said clamping and supporting action but is merely to be regarded as surplus material. The fin is removed in the further processing of the semi-finished product.

It is also available for the blank to be shaped, e.g. by forging, from material with a smooth, e.g. ground and polished surface, providing satisfactory and accurate surfaces in the further processing, this being again a condition for the desired supporting effect. After the removal of the fin, therefore, all that is necessary is to remove the relatively thin outer skin of reduced hardness, which can be done, for example, by grinding it off. Blades produced by this method lend themselves excellently to the polishing process.

The invention also proposes a stainless steelknife blade characterized by the fact that it consists of the core of a blank which has first been forged and then further processed by the cold shaping method, the material of which this blank is made consisting of stainless steel, such as 18/8 steel, which in the initial state takes the form of a cleavage product with a ground surface.

A blade of this kind can be produced particularly advantageously from a blank which, in accordance with the invention, is characterized by an extra accumulation of material in the zone of the cutting edge of the finished blade, i.e. the blank possesses, in contrast to blanks of the known kind, far more material in the place where the finished blade is to be thinnest. The purpose of this at first sight contradictory suggestion is to ensure that the material present in the core of the said accumulation will be reliably prevented, by the supporting effect of the surplus material, from flowing, as a result of the shaping operations, but that comparatively moderate deformation energy will nevertheless be sufficient, because it is only where a high and permanent degree of hardness is in any case required that an extra amount of material Q will be present, to be removed in due course by removing the fin and by re-grinding. The blank will thus be provided, mainly in the zone of the cutting edge of the finished blade, with a greater cross-sectional area than in the zone which will correspond to the back of the knife.

DESCRIPTION OF THE DRAWING The invention will be described in detail with reference to the accompanying drawings in which:

FIG. 1 is a side view of a blank produced by the hot shaping process;

FIG. 2 is a plan view of the blade blank shown in FIG. 1;

FIG. 3 is a cross-section along the line III=III of FIG. 1, on a larger scale;

FIG. 4 is a similar cross-section to that shown in FIG. 3, through a semi-finished product made from the blade blank, and likewise on a larger scale.

DESCRIPTION OF A PREFERRED EMBODIMENT The blank shown in FIGS. 1 to 3 has an approximately rectangular cross-section in the zone of the cutting edge 2, as shown in particular by FIG. 3. At the front lower end of the blade, i.e. in the part where the cutting edge will eventually be situated, is an extra accumulation of material 3, which is nevertheless confined to a comparatively small part of the blade. With a forging temperature of 600 C., for example, a knife blade can be forged with a drop energy of 2,000 mkp. This not only results in the shape shown in FIGS. 1 to 3 for that part of the blank which will eventually correspond to the blade but also ensures the production of the bent part 4 at the end of the blade, and the hot forging process alone sufiices to impart to the material a noticeably firmer structure by comparison with the initial characteristics.

The fin is followed by a tongue 5 by means of which the blade can be inserted in a handle and secured there in. It is also possible, however, to produce the blade and the handle in one single piece or to connect the blade to the handle by some other method.

FIG. 4 shows how the blank illustrated in FIGS. 1 to 3 is further processed. The shaping of the blank 1 is accompanied by the deliberate formation of a kind of fin 7 around the actual blade 6, particularly in the zone corresponding to the cutting edge, which is to be regarded as the flow zone. This fin 7 functions during the shaping process as a kind of grip or clamp around the actual blade 6, illustrated in broken lines in FIG. 4, so that the material in the core of the blank ll does not flow during the shaping process but is consolidated still further.

As may be clearly seen from FIG. 4, the actual blade 6 consists of the core of the semi-finished product, which is exposed, e.g. by a grinding process, after the completion of the shaping. The grinding process, according to the invention, not only serves to counteract any inaccuracies in the surface but also contributes considerably to the exposure of the hard core of the semi-finished product. The

4 outer skin to be removed need not be thicker, in general, than fractions of a millimetre.

The blank used in accordance with the invention for the production of knife blades or similar objects has quite a different shape from the blanks employed in the production of knife blades by the known method. The familiar shape of the knife does not appear until after the final processing.

While the foregoing description has been substantially confined to the production of table knife blades, it will be appreciated that the invention is applicable to all types of stainless steel blades, whether intended for hand knives, other hand tools or machinery utilising knife blades.

Having described the invention, what is desired to be secured by Letters Patent is:

l. A method of manufacturing a stainless steel knife blade having a finished cutting edge of predetermined shape and volume comprising the steps of (a) forming a blank of stainless steel having an edge forming portion of substantially greater volume than said finished cutting edge,

(b) deforming said edge forming portion to establish an inner very hard core surrounded by an outer softer fin,

(c) removing selected portions of said softer fin to expose said very hard core,

(d) shaping said exposed very hard core into said predetermined shape of a cutting edge.

2. The method of claim 1, in which said blank is formed of 18/8 stainless steel.

3. The method of claim 1, in which (a) said inner core is hardened to approximately 42-50 R and (b) said fin is hardened to approximately 35-42 R 4. The method of claim 1, in which (a) said core is not shaped beyond its flow limit, and

(b) said fin is shaped beyond its fiow limit.

5. The method of claim 1, characterized in that (a) said blank forming step is effected by hot working,

and

(b) said blank deforming step is effected by cold working.

6. The method of claim 1, in which said fin removal step is effected by grinding.

References Cited UNITED STATES PATENTS 361,620 4/1887 Dunn 76104 3,218,892 11/1965 Fresch et a1. 76104 FOREIGN PATENTS 580,579 7/1933 Germany 76-104 BERNARD STICKNEY, Primary Examiner US. Cl. X.R. 30-350; 76l01 

